1) Field of the Invention
This invention relates to a leak detection system for gas, steam or the like, said system being suitable for the detection of gas, steam or the like leaking from equipment or apparatus of a plant where a flammable or noxious substance is handled in a gaseous, liquid or solid form, as well as to a method for the measurement of the direction and velocity of local wind, said measurement being needed for the estimation of a leak point and leak quantity, and an instrument for the determination of wind direction and velocity.
2) Description of the Related Art
From every country there are reports of serious accidents or disasters caused by fire, explosion or leakage of noxious gas from individual machines, equipment or facilities, arising at factories with a plurality of machinery, equipment and/or facilities connected together via pipes, or in industrial complexes where a conglomeration of such factories is systematically linked one to another. Damage caused by such incidents is not limited to the loss of facilities and/or interruption of production. For example, accidents at nuclear power plants and the like where radioactive substances are handled involve such potential danger that they may even lead to global contamination.
Causes of accidents include those pertaining to human error in operation and those attributed to a failure of machinery, equipment or facilities. In a large majority of reported incidents, leakage of gas or the like actually took place as an initial phenomenon; the gas so leaked then igniting due to the existence of a certain ignition source, resulting in fire or explosion.
It is, therefore, possible to obviate many of such accidents and to minimize the loss of property of the society, if leakage of gas or the like can be discovered and stopped in an early stage, when the quantity of leakage is still small.
With the foregoing objective in view, business establishments beyond a certain size are required to install gas leak detectors under laws such as the Fire Protection Law and High Pressure Gas Control Law in Japan. In particular, according to Section 8, No. 53 of the Safety Regulations for Industrial Complexes in the latter law, it is specifically ruled that gas leak detectors of a prescribed specification be installed at intervals of 20 m, with at least one gas leak detector at each point of installation along the boundary of each plant or the like.
Besides these statutory regulations, business establishments which manage factories or various facilities have of their own volition also exercised tremendous efforts for the early discovery of leakage of gas.
To date there exists neither a highly reliable leak detection method for the discovery of leakage of gas, steam or the like nor a system for estimating the point, quantity and the like of leakage when such leakage is discovered. Indeed, such detection is commonly dependent only on discovery by a maintenance crew member on regular patrol in a plant in an effort to discover any abnormality.
Under these circumstances, the probability of detection of gas leakage in a plant by plural gas detectors discretely arranged in the plant is therefore very low. Moreover, even if a detector provides a warning, the retention of a warning signal may be brief and often becomes intermittent. It is, therefore, difficult to determine if the firm warning results from discovery of a real leakage or is caused by some noise or is due to drifting of the zero point and, under the circumstances, the detection of gas leakage relies upon human judgment.
It is typical for conventional wind direction and velocity indicators to be in the form of a model plane which rotates horizontally around a vertical axis, and to be equipped with a propeller at a free end of a horizontal portion. In general, owing to the provision of a tail, the direction of the main body of the plane is brought into conformity with the direction of wind so that this directional change indicates the wind direction. Further, the propeller rotates at a revolution speed proportional to the velocity of the wind and the resulting rotation is transmitted to a small generator accommodated inside the main body of the plane. The wind velocity is therefore indicated by the output voltage of the generator.
The conventional wind direction and velocity indicators of the type described above are however accompanied by the drawback that they do not operate sufficiently well at low wind velocities. At a wind velocity not higher than 1 m/sec, for example, rotation is so slow that the accuracy of indication of the wind direction and velocity becomes poor. Further, at 0.5 m/sec or lower, the propeller virtually stops, thereby making the measurement no longer feasible.
Another drawback of the conventional type resides in the difficulty in constructing the indicators in an explosion-proof form which enables them to be used in an atmosphere having potential fire and/or explosion hazard, and this difficulty limits their use at places where a chemical reagent, petroleum product, gaseous fuel or the like is handled. Although their production in an explosion-proof structure is feasible, this leads to the disadvantages that they are expensive and, if a seal is provided between a propeller and a small generator as a common means for providing an explosion-proof construction, the resultant extra friction further downgrades the accuracy of wind velocity measurements.
Although the need for the measurement of wind velocities as low as 1 m/sec and slower in the field of general meteorological observation is not referred to in the present specification, there is an increasing demand for the high-accuracy measurement of such low wind velocities in order to determine the wind direction and velocity for environmental assessment at factories, offices and the like, especially in order to predict the state of diffusion of noxious gas, steam or the like at such places in the event of its leakage and also to estimate the point of the leakage. Further, to measure the wind direction and velocity in such a case, it is essential to employ wind direction and velocity indicators which are usable in an atmosphere having potential fire and/or explosion hazard or can be modified into an explosion-proof construction without impairing their measurement accuracy.